Discovery may lead to better lure to detect fruit fly

(Phys.org) -- A certain species of yeast that UC Davis researchers found in "almost all" their samples of raspberries and cherries infested by the spotted-wing drosophila (Drosophila suzukii) may lead to a better lure to detect the invasive pest in the field.
A research team from the UC Davis Department of Entomology, the Department of Food Science and Technology, and a visiting professor from the University of Extremadura, Spain, found that the yeast, Hanseniaspora uvarum, appeared in just about every cherry, raspberry, and larva of the spotted-wing drosophila (SWD) that they sampled at collection points in Davis, Winters, and Watsonville.

The agricultural pest, native to southeast Asia and now found in many parts of North America, was first observed in California in fall 2008 in the Central Valley, but was not identified until early 2009. It is reported to attack soft-skinned, ripening fruits, and has been a particular problem for raspberry and cherry growers in California.

The research team  comprised of Phaff Yeast Culture Collection curator Kyria Boundy-Mills of the UC Davis Department of Food Science and Technology; entomology professor and integrated pest management specialist Frank Zalom; graduate Ph.D. student Kelly Hamby in the Zalom lab; and UC Davis visiting professor Alejandro Hernandez of University of Extremadura, Spain  published their work in a recent cover article of the journal Applied and Environmental Microbiology, the No. 1 cited journal in microbiology.

"This represents the first look at potential yeast associations of Drosophila suzukii," said Hamby.

"We are now testing to see if this species will be a good lure to detect this fly in the field," Boundy-Mills said.

"When we started the work we hoped to find candidate yeast species that could be used to improve the bait in Drosophila suzukii traps," Hamby said. "Fruit flies are regularly trapped with apple cider vinegar or baker's yeast and sugar plus water so these were the traps that were originally recommended for monitoring when SWD first invaded California in 2008."

"Unfortunately, these lures trap all fruit flies, and many other non-target insects, so the hope was that we might be able to design a more selective and attractive lure by identifying a more specific yeast that is used by SWD," Hamby said.

"Often Drosophila have interactions with yeast communities, and communities often vary between host plant species, so it was a bit of a surprising that we found Hanseniaspora uvarum so often, though, we used only culture-based methods so other yeasts may be present that are hard to culture," Hamby said.

Hannah Burrack, a former Zalom lab graduate student (now an assistant professor and Extension specialist in the Department of Entomology, North Carolina State University) originally found that olive flies were more attracted to yeasts that were isolated from the flies themselves than to the Torula yeast bait that is commercially available for olive fruit fly management, Hamby said.

Yeast ecologists have investigated Drosophila-yeast interactions for more than 60 years, Hamby said. "The work that had been done with Drosophila was the impetus for Hannah Burrack's work, therefore, we thought that we really had a great study system in SWD."

Zalom and Burrack had earlier collaborated with Boundy-Mills, "so our lab already had an established collaboration with a yeast systematist before we dreamed up this project," Hamby noted. "Kyria curates a huge UC Davis yeast collection and all the yeast strains we found were deposited into the Phaff collection."

Boundy-Mills pointed out that SWD is causing major crop damage to soft fruits such as berries and that better detection and control methods are needed.

In their journal article, the authors wrote that "D. suzukii is unique in that it oviposits on marketable fruit relative to overripe or damaged fruit, and its injury facilitates colonization by other Drosophila species. If untreated, it is capable of causing a potential $860 million of revenue loss annually to blackberries, raspberries, and cherries in California, Oregon, and Washington. Knowledge of potential yeast associations could be used in lure development."

Zalom said the pest is a major problem in the area for backyard cherries. "Many residents have not been able to harvest cherries for several years now."

For the cover photo, Hamby created a Drosophila suzukii drawn with yeasts on potato dextrose agar. "Eyes and wing spots were drawn with Rhodotorula mucilaginosa, while Rhodosporidium toruloides and the Drosophila suzukii-associated yeast Hanseniaspora uvarum were used for the outline and the interior, respectively," according to the photo caption in the journal. The photo was taken by Kathy Keatley Garvey, UC Davis Department of Entomology.